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United States Patent |
6,240,934
|
Durst
,   et al.
|
June 5, 2001
|
Method and device for treating holes or recesses extending into workpieces
with liquid treatment media
Abstract
The treatment, for example the cleaning of holes or recesses in workpieces,
is problematic when the holes or recesses have an opening width of below
0.5 mm, and especially when the latter do not penetrate the workpiece
(blind bores). In known methods, gas bubbles adhering to the side-walls of
holes of this type cannot be removed or liquids situated within the holes
cannot be effectively exchanged.
With the method according to the invention an effective exchange of the
liquid contained in the holes and situated outwith the holes is made
possible. For this purpose the liquid treatment means is sprayed as a jet
into the holes, said jet having a diameter which is smaller than that of
the holes.
Furthermore, a device is described for carrying out this method which is
characterised by a nozzle with one or several nozzle discharge openings
with a diameter below 0.5 mm, by a liquid supply unit by means of which
liquid treatment medium is pumped through the nozzle discharge openings
and by a filter unit, communicating with the openings and the feeder unit,
for removing particles from the treatment medium.
Inventors:
|
Durst; Franz (Langensendelbach, DE);
Brenn; Gunter (Erlangen, DE);
Schafer; Michael (Numberg, DE);
Meyer; Heinrich (Berlin, DE);
Streup; Heribert (Berlin, DE)
|
Assignee:
|
Atotech Deutschland GmbH (DE)
|
Appl. No.:
|
036107 |
Filed:
|
August 16, 2000 |
PCT Filed:
|
September 6, 1996
|
PCT NO:
|
PCT/DE96/01716
|
371 Date:
|
August 16, 2000
|
102(e) Date:
|
August 16, 2000
|
PCT PUB.NO.:
|
WO97/11209 |
PCT PUB. Date:
|
March 27, 1997 |
Foreign Application Priority Data
| Sep 06, 1995[DE] | 195 34 521 |
Current U.S. Class: |
134/2; 134/22.18; 134/23; 134/32; 134/152; 134/166R; 134/167R |
Intern'l Class: |
B08B 003/02; 109; 110; 111; 902; 166 R; 167 R; 168 R; 169 R; 152; 198; 199; 144; 171 |
Field of Search: |
134/2,22.1,22.11,22.12,22.13,22.14,22.16,22.17,22.18,23,25.5,32,104.2,104.3
|
References Cited
U.S. Patent Documents
4119439 | Oct., 1978 | Boucher | 134/183.
|
4559664 | Dec., 1985 | Bohme et al. | 134/171.
|
4789405 | Dec., 1988 | Blasing et al. | 134/1.
|
5190065 | Mar., 1993 | Kovac et al. | 134/107.
|
5246023 | Sep., 1993 | Breunsbach et al. | 134/57.
|
5366562 | Nov., 1994 | Schwarze et al. | 134/169.
|
5778911 | Jul., 1998 | Yoshio | 134/104.
|
5891257 | Apr., 1999 | Stephanie et al. | 134/5.
|
Foreign Patent Documents |
3305564 | Mar., 1984 | DE.
| |
35 28 575 | Feb., 1987 | DE.
| |
36 24 481 | Jan., 1988 | DE.
| |
36 38 630 | May., 1988 | DE.
| |
3708529 | Sep., 1988 | DE.
| |
39 05 100 | Aug., 1990 | DE.
| |
Primary Examiner: Coe; Philip R.
Attorney, Agent or Firm: Paul & Paul
Claims
What is claimed is:
1. Method for treating holes or recesses extending into workpieces with an
opening width below 0.5 mm using a liquid treatment medium emerging from a
nozzle, characterised in that a jet of the treatment medium with a
diameter, which is smaller than the opening width, is directed into the
holes or recesses.
2. The method according to claim 1, characterised in that the jet of the
liquid treatment medium is directed through a liquid on to the workpieces
situated in said liquid or through a gas space on to the workpieces
situated in this gas space.
3. The method according to one of claims 1-2, characterised in that the
workpiece and the jet are moved relative to one another so that the jet of
the treatment medium washes over the surface of the workpiece and is
directed into the holes or recesses one after another.
4. The method according to one of claims 1-2, characterised in that several
jets of the treatment medium are directed simultaneously and parallel to
one another on to the surface of the workpiece and into the holes and/or
recesses.
5. The method according to one of claims 1-2, characterised in that the
nozzle is moved backwards and forwards transversely to the relative
movement and parallel to the surface of the workpiece or in a circular or
elliptical path parallel to the surface of the workpiece.
6. The method according to one of claims 1-2, characterised in that circuit
boards are directed past the nozzle in a horizontal position and
horizontal direction at a short spacing.
7. The method according to one of claims 1-2 wherein the workpieces are
circuit boards provided with clearance holes and/or blind bores.
8. Device for treating holes or recesses extending into workpieces with an
opening width below 0.5 mm using a liquid treatment medium emerging from a
nozzle, wherein a jet of treatment medium is provided having a diameter
that is smaller than the opening width, characterised by a nozzle (9) with
one or several nozzle discharge openings with a diameter below 0.5 mm,
with a liquid distribution unit (10), by means of which liquid treatment
medium is pumped through the nozzle discharge openings and with a filter
unit (12), communicating with the openings and the distribution unit, for
removing particles from the treatment medium (11).
9. The device according to claim 8, characterised in that, the nozzle
discharge openings taper in the direction of the treatment jet (5).
10. The device according to one of the claims 8 or 9, characterised by
several nozzle discharge openings in a matrix arrangement in an
essentially flat nozzle head.
11. The device according to claim 10, characterised in that, the nozzle
discharge openings are arranged in the nozzle head in several rows which
are offset against one another.
12. The device according to any one of claim 8 or 9 characterised by a
distribution chamber (16) for the treatment medium, said distribution
chamber evening out the amount of treatment medium (11) flowing through
the individual nozzle holes and being located in front of the nozzle
discharge openings.
13. The device according to claim 12, characterised by means for moving
circuit boards (7) horizontally which are arranged in a horizontal
position relative to the nozzle (9).
14. The device according to claim 13, characterised in that, several
nozzles (9',9") are arranged between transportation devices (14',14") by
means of which the circuit boards (7) are moved and in that, the nozzles
(9',9") extend at least over the entire width of the circuit boards (7).
15. The device for treating clearance holes and blind bores in circuit
boards according to any one of claim 8 or 9, characterised in that the
nozzle discharge openings in an essentially flat nozzle head are arranged
in several rows which are offset against one another, and in that the
offset between adjacent rows or a multiplicity of said offset roughly
corresponds to the spacing of the clearance holes and/or blind bores from
one another.
16. The method according to claim 1, wherein the diameter of the jet is
smaller than half the opening width.
Description
SPECIFICATION
The invention relates to a method and to a device for treating very small
holes or recesses extending into workpieces with liquid treatment media.
Should workpiece surfaces be treated with liquids, the surfaces are as a
rule brought into contact with the treatment media by immersion. Typical
examples of usage are represented by the cleaning of substrates, for
example of covering pieces, the electroplating treatment of metal parts
and plastic material parts and also the electro-plating procedures in the
production of circuit boards.
In many areas of technology thin metal layers are applied to the surfaces
of materials, in order to impart to the surfaces certain properties, which
are required for the use of materials in cases of industrial application.
Although there is already a multitude of varying coating techniques
available, electro-plating metal plating methods still represent important
treatment methods despite the frequent occurence of problems specific to
the procedure.
For example, problems can arise, when workpieces with very small holes or
with other recesses, which extend into the surface of the workpieces and
have small dimensions, are to be treated with liquid medium. In this case
these holes and recesses are not adequately or not at all washed through,
with the result that the desired treatment cannot be achieved.
In circuit board technology for example the sides of the holes, which
extend through the circuit board laminate or which are inserted as blind
bores, are provided with a metal layer. For this purpose, after being
produced, for example by drilling, these holes or recesses have firstly to
be cleared of impurities generally, for example of resin smears caused by
boring on the drilled hole wall while the circuit board is brought into
contact with etching agents. Furthermore, chemical solutions with
surface-active substances (wetting agents) are inserted also for cleaning
the holes. After cleaning, the electrically insulating drilled hole walls
are activated with solutions containing a noble metal and subsequently are
copper-plated or nickel-plated, as a rule with electroless metallization
solutions. Then a metal layer with a thickness of roughly 20 .mu.m is
deposited by means of electrolytic plating on the wall surfaces of the
holes.
Because of the miniaturisation of circuit structures on circuit boards,
smaller and smaller holes are being formed, for example with a diameter of
0.2 mm, in circuit boards, which still need to be reliably plated. For
this reason there exist various methods for removing air from these holes
and ensuring an adequate exchange of liquid between the inside of the hole
and the liquid treatment medium outwith the holes. Special methods are
employed for flushing out these very small holes.
In the German Patent document DE 35 28 575 A1 there is known, for this
purpose, a method for cleaning, activating and/or plating boreholes in
horizontally placed circuit boards, in which the circuit boards run over a
drenching line at a constant speed, said line being formed by a jet
arranged beneath the travelling line and perpendicular to the direction of
movement, and in which the liquid treatment medium is conveyed in the form
of a vertical wave to the underside of the circuit board and also a device
for carrying out this method is known.
Further papers have been published on this method describing special
applications for flushing out drilled holes in circuit boards (for example
in DE 36 38 630 A1, DE 36 24 481 A1).
Another solution can be drawn from the German Patent document DE 39 05 100
C2, in which a method is given for the chemical and electrolytic surface
treatment of board-shaped workpieces, which are furnished with small
openings, in aqueous solutions, the workpiece having two autonomous
vibration movements which are independent of one another. The first of the
two vibration movements extends perpendicular to the surface of the
workpiece and the second in roughly the same direction as the first and at
the same time as the latter, the frequency of the first movement being
essentially lower than the frequency of the second, representing a heavily
pulsating oscillation in quick sucession. The amplitude of the first
vibrating movement is essentially greater than the amplitude of the
second.
Numerical simulations for determining the flow conditions in drilled holes
of circuit boards have shown in addition that oscillations of that type,
orientated perpendicular to the surface of the circuit boards, assist the
liquid exchange more effectively than oscillations which have vibration
components exclusively parallel to the circuit board surface.
However the mentioned solutions to the problem of reliably treating very
small holes and especially blind bores are not suitable, since, in these
cases, the flow only works in the entry region of the holes. Blind bores
and other recesses extend only to a definite depth in a workpiece or solid
body. Apart from problems arising also from very small clearance holes,
the problem exists here as well in that the liquid flowing in must also
flow out again to attain an adequate liquid exchange. Otherwise, at best a
very slow material exchange would be possible by means of diffusion.
Because of the boundary layer adhering to the hole wall or because of a
finite viscosity from applicable treatment liquids, a through-flow by
means of vibration movements cannot be produced in these holes at a depth,
which for example, when using aqueous treatment liquids, corresponds
approximately to the diameter of the hole.
In order to treat circuit boards with blind bores it is normal for example
to treat the circuit boards in a device, in which the circuit boards are
introduced in a horizontal position and horizontal direction through a
treatment chamber; the circuit boards being situated within the treatment
liquid during passage. In this way, it can at least be achieved, that gas
bubbles which are situated in the holes on the top of the circuit boards
can be removed relatively simply. A reliable exchange of material within
the time available for treatment and particularly the removal of the gas
bubbles from the holes on the underside of the circuit boards is however
not possible with this method. Moreover even gas bubbles can no longer be
removed with certainty, using this method, from holes in which the ratio
of hole length to hole diameter exceeds a value of approximately 1.
Hence the problem underlying the invention is to avoid the disadvantages of
the state of the art and particularly to find a reliable method and a
device suited to the purpose of flushing holes provided in workpieces and
other tiny hollow spaces, opening outwards, and also recesses with an
opening width below 0.5 mm with a liquid treatment medium. In particular,
a method and device for treating circuit boards provided with blind bores
is to be produced.
The solution to the problem consists in directing a liquid jet of the
treatment medium on to the surface of the substrate to be treated which
has a diameter which is smaller than the opening width of the holes or
recesses, i.e. in drilled holes of the diameter of the holes to be treated
in the surface of the substrate. By substrate is meant any solid body or
workpiece to be treated. By means of this it is possible to direct a flow
of treatment medium into the inside of the holes and recesses such that an
effective rinsing of the blind bore is also achieved even when these holes
have a very small diameter, for example of 75 .mu.m. The jet directed into
the inside of the recess is reversed at its base, so that, within the
hole, jets of treatment medium which are directed outwards are also
formed.
According to the invention, this is effective primarily when the jet of
treatment medium has a diameter, which at most amounts to half the
diameter of the hole. If a jet has a diameter which is greater than the
diameter of the hole, then the flow effect, according to the invention,
can no longer be achieved in the hole.
With the aid of the subsequently described drawings and figures, the method
according to the invention is explained and the device is shown
schematically or details of the device are depicted by means of
photographic figures, which show;
FIG. 1: Cross-section of a blind bore in a circuit board, shown
schematically;
FIG. 2: Flow conditions in a blind bore, computer simulation;
FIG. 3: Stability curve of a jet of treatment medium in air, shown
schematically;
FIG. 4: View of the nozzle discharge openings in a multi-hole nozzle,
photograph from a scanning electron microscope;
FIG. 5: Device according to the invention, shown schematically;
FIG. 6: Nozzle chamber with several nozzle openings, shown schematically;
FIG. 7: Nozzle opening, photograph from a scanning electron microscope;
FIG. 8: Treatment unit for the horizontal treatment of circuit boards,
schematic side-view.
In FIG. 1 the self-adjusting flow conditions in a blind bore in a circuit
board are shown schematically. If the jet of treatment medium 5 is
directed centrally and along the hole axis into the preferably cylindrical
hole 1 (hole length 1, hole diameter d) through the hole entrance 2 of a
circuit board 7, the distribution of the flow within the hole, which is
shown schematically, arises. The individual arrows 6 characterise local
flow components. The jet 5 which is directed downwards is reversed upwards
at the base of the hole 3. In this way a strong toroidal flow which is
directed outwards arises along the wall 4 of the hole to be treated, so
that gas bubbles, which adhere there through surface tension, are removed
from the walls. Furthermore, the material transporter means, which is
required for the treatment of the walls and the base of the hole, is also
made possible in this way, through which material transporting means used
materials are removed and materials required for the treatment are
delivered. These flow components accumulate near the hole surface area and
form an essentially toroidal flow profile 8 which is directed out of the
hole.
If it concerns longitudinal holes in the recesses, the jet of treatment
material is directed preferably essentially parallel to the longitudinal
axis of the holes.
In a numerical simulation procedure according to the principle of finite
volumes method (for example described in: E. Noll, Numerical flow
technology ,Springer-Verlag Berlin, New York, 1993), flow conditions in a
blind bore are represented graphically. In FIG. 2 a section through a
blind bore 1 in a circuit board 7 is reproduced here and also the
direction of the individual flow components in the hole, marked by arrows
6. The liquid jet 5, which is directed into the hole, is in this case not
aligned quite centrally and is slightly deflected by the flow components 6
which are directed upwards and formed by reversal in the base of the hole
3. Nevertheless a flow profile is constructed which is adjacent to the
walls 4 of the hole and directed outwards to the hole entrance, so that
the operation according to the invention results.
The advantageous effect according to the invention is only achieved when
the jet diameter is smaller than the opening width of the recesses to be
treated. Particularly good results are achieved when the jet diameter is
smaller than half the opening width of the recesses or of the diameter of
the holes.
On the other hand the flow speed in the inside of the hole decreases again
in the case of very small jet diameters, since the available impulse of
the jet, which is directed into the hole, is then smaller. This effect is
reproduced in Table 1. Liquid jets with varying diameters were directed
into a hole with a diameter of 0.3 mm and a depth of 0.8 mm using various
jet speeds. The effect, according to the invention, of the rinsing is
represented by the speed of the liquid (speed at the base), which adjusts
immediately above the base of the hole.
Maximum effect is achieved in the portrayed case when the diameter is about
0.1 mm (approximately 35% of the diameter of the hole). A very great
reduction in the effectiveness of the flow within the hole can be observed
when the jet diameter exceeds 0.16 mm (53% of the hole diameter) up to 0.2
mm (67% of the diameter of the hole). Even smaller changes in the diameter
at larger values cause drastic effects. The same is also true for a change
in the jet diameter from 0.05 mm (.DELTA.17%) to 0.025 mm (.DELTA.8.3%).
The effect according to the invention is negligible when the jets are
discontinuous or rather fall as single droplets as they pass the entrance
to the hole.
The fine jets of liquid can be produced by discharging the treatment medium
from appropriate nozzles. For this purpose, sufficiently fine holes are
inserted as nozzle discharge openings, or in general a jet production
device configuring a nozzle, into a nozzle chamber, into which the liquid
treatment medium flows. In order to produce the jets the liquid is
pressurised. The stability of the liquid jets against the formation of
droplets depends on various factors:
The invention avails itself then of known technology for the construction
of laminar jets on the other side of the nozzle opening. (M. J. McCarthy,
N. A. Molloy, Review of Stability of Liquid Jets and the Influence of
Nozzle Design, The Chemical Engineering Journal, Volume 7 (1974) Pages
1-20). The jets tend fundamentally, in a gaseous environment, to break
into droplets after a definite operating length (dispersal length L) i.e.
at a definite distance from the nozzle discharge opening. This tendency is
influenced primarily by the surface tension of the liquid emerging from
the nozzle openings relative to the medium surrounding the free jets.
Dependent upon the non-dimensional Weber number We of the liquid jets,
various large dispersal lengths are observed. A characteristic
relationship of the dispersal length L to the discharge speed v of the
liquid from the nozzle opening is depicted in FIG. 3. According to that,
there results a complicated dependency of the dispersal length L to the
discharge speed. Only in the lower speed region is there a relation
between the dispersal length roughly proportional to the speed v.
The dispersal length cannot therefore be selected irrespective of the
Reynolds number Re of the liquid jet, when a certain type of liquid is
used. For the use of free jets according to the invention, the dispersal
length L must be as great as possible to ensure the formation of a
continuous liquid jet between the nozzle and the workpiece surface to be
treated or the holes and recesses contained within it. The non-dimensional
parameter which is characteristic of the dispersal length L is the Weber
number We, which is dependent upon the density .rho. of the liquid
treatment medium, the surface tension .sigma. of the treatment medium, the
discharge speed v and the discharge diameter d of the jet of the treatment
medium in the following way:
We=v.sup.2.multidot.d.multidot..rho..multidot..sigma..sup.-1,
TABLE 1
Jet Jet Base
Test Speed diameter Speed
No. [m/s] [mm] [m/s]
1 3.0 0.1 0.45
2 1.5 0.2 0.01
3 1.5 0.16 0.1
4 1.5 0.14 0.12
5 1.5 0.1 0.22
6 1.5 0.05 0.1
7 1.5 0.025 0.01
For tubular nozzles, the non-dimensional dispersal length L/d is a function
of the square-root of the Weber number We.
A dispersal length of a few centimeters can be achieved for example, if a
jet diameter of 150 .mu.m is formed and if an aqueous liquid jet is
produced under pressure from an appropriate nozzle opening into a gas, for
example into air. The Weber number takes on the value We=206.9, so that
We=14.4, when an aqueous treatment medium with a discharge speed of v 10
m/s and a discharge diameter of d=150.10.sup.-6 m is sprayed into the air
(.sigma.=72.5.multidot.10.sup.-3 N/m,.rho.=1 g/cm.sup.3. In this case a
non-dimensional dispersal length of L/d=86, i.e. the dispersal length L of
12.9 mm is attained. Within this distance the jet is homogenous and does
not disperse into individual droplets. A substrate, which is to be treated
and which is arranged at a spacing of less than this length from the
nozzle discharge opening, is struck by a fine jet with a jet diameter of
approximately 150 .mu.m, in order that the effect according to the
invention can be achieved.
If the aqueous treatment medium is not sprayed on the other hand into a
gaseous atmosphere but into a liquid, other conditions arise since the
Reynolds number of the jet represents the characterising parameter in this
case. If the liquid is used as a liquid through which the jet of treatment
medium is sprayed into the holes of the workpiece which is likewise
situated in this liquid with which the workpiece is to be treated then the
jet no longer disperses into individual droplets, since the surface
tension .delta. is approaching zero. In this case on the other hand, the
jet expands a little because of the higher viscosity of the medium
surrounding the nozzle.
Hence a preferred embodiment is represented by a variation on the method,
in which the workpiece to be treated is situated in the liquid treatment
medium and in which the nozzle discharge openings, facing the workpiece
surface closely, are likewise submerged in the treatment medium, since in
this way very fine, stable jets can be produced.
In order to treat circuit boards, in which clearance holes and blind bores,
which are distributed over the entire surface, are situated, it is further
advantageous to move the circuit board and the nozzle continuously
relative to one another. For example, the circuit board could be moved in
a horizontal position and horizontal direction and preferably at a short
distance past a stationary nozzle. On the other hand it is also possible
to move the nozzle past the circuit board, for example if the circuit
board is attached to a framework in a vertical fashion and submerged
together with the latter into a treatment bath. In this way, the treatment
liquid for improved flushing out from the nozzle discharge openings, which
are located within the treatment medium, is directed on to the circuit
board surface and into the holes. In both cases the jet of treatment
medium washes over the surface of the circuit board and is thereby
directed into the individual holes in the circuit board one after another.
In both application cases with linear direction of relative movement it is
also advantageous to provide several nozzle discharge openings e.g. at the
spacing of the holes beside one another in an appropriate device. In FIG.
4 a further example is shown for a circular arrangement of a multiplicity
of very fine openings of approximately 60 .mu.m diameter per nozzle head.
In another embodiment several rows can also be provided with nozzle
discharge openings, which are offset against one another, for example in
an essentially flat nozzle head. In this way, several jets of treatment
medium can be directed simultaneously and parallel to one another on to
the circuit board surface and into the holes. The spacing of the
individual holes must not however remain under a critical minimum spacing,
since the liquid jets tend to merge with one another.
In order to direct the liquid jets accurately and uniformly also into
clearance holes and blind bores in circuit boards, the nozzle discharge
openings in the nozzle head can be arranged in several rows and offset
against one another such that the offset between adjacent rows or a
multiple of this offset corresponds roughly to the spacing of the
clearance holes and/or blind bores.
With arrangements of this sort with several nozzle discharge openings in
the device according to the invention it is possible to treat the
individual holes in the circuit board by passing them over the nozzle with
the free jets of liquid jets.
If the grid of nozzle openings which are arranged in a matrix does not
accord with the grid of the holes arranged on the circuit board,
individual holes will still not be struck by the free jets when the
circuit board moves over the nozzles. In this situation, the nozzles can
also be moved backwards and forwards, parallel to the circuit board
surface and transversly to the relative movement of the circuit board to
the nozzles. Instead of a backwards and forwards movement the nozzles can
also be moved in a circular or elliptical path parallel to the surface of
the circuit board.
In order to carry out this procedure, a device with one or several nozzles
is inserted. The device, shown schematically in FIG. 5, comprises two
nozzles 9 with respectively one or several nozzle discharge openings with
a diameter under 0.5 mm, in addition a liquid supply unit, typically a
pump 10, by means of which liquid treatment medium is pumped through the
nozzle discharge openings, and a filter unit 12, communicating with the
openings and the supply unit, for removing particles from the treatment
medium. Immediately beside the nozzle discharge openings, the workpieces
to be treated, in this case circuit boards 7, are either located in a
stationary manner or the workpieces are passed over nozzles, by means of
appropriate transport medium which is directly next to the nozzle
discharge openings.
In order to prevent the very small discharge openings being blocked by
particles in the treatment liquid, the liquid must also be very carefully
freed of very fine particles or impurities before discharging from the
nozzle. For this purpose, the filter unit 12 is provided. Furthermore, the
liquid is freed of entrained gas by means of a bubble trap 13 before
entering into the nozzles, in order to prevent the jets being disturbed by
gas escaping out of the openings.
In order to produce sufficiently stable and fine free jets, nozzles are
provided with very fine nozzle discharge openings, for example with a
diameter of 0.02 mm to 0.5 mm. The diameters and the grid spacing of the
individual nozzle holes can be fitted to the diameter and the grid spacing
of the holes in the circuit boards. For this purpose, appropriate hollow
pieces, for example, with openings preferably on a flat side (nozzle head)
are used (FIG. 6). The nozzle openings are produced for example by laser
drilling. The holes can be produced also by means of a chemical etching
process by applying a stable photosensitive resist against the etching
means on to the surface, in which the holes are to be etched, said resist
being exposed with the hole pattern and the holes being formed after
developing with suitable etching means.
The liquid jet 5 is produced by the nozzle discharge openings, which are
situated on the underside of the nozzle. For this purpose, the liquid 11
is fed into the nozzle under pressure from above.
The shape of the discharge openings is likewise critical for the quality of
the free jets which are formed. Particularly openings (FIG. 7) which taper
in the direction of the jet 5 of treatment medium ensure that the speed
distribution of the liquid in the jets has no radial non-homogeneities so
that the jets tend to expand or disperse into individual droplets only to
a small extent.
If nozzles with matrix-like nozzle discharge openings, which are arranged
in several rows are used, it must, furthermore, be seen to, that all
liquid jets emerge from the openings with roughly the same pressure. If
this is not the case constant results cannot be achieved. For this
purpose, there is a distribution chamber 16 in the nozzle, through which
the treatment medium flows before penetrating through the discharge
openings, with the result that the quantities of treatment medium passing
through the individual holes are evened out. The constructional design of
distribution chambers of this type is possible according to the principal
points, which are described extensively in; F. Durst, U. Lange and H.
Raszillier, Optimisation of Distribution Chambers of Coating Facilities,
Chemical Engineering Science, Volume 49(1994),Part 2, Pages 161-170.
Circuit boards can be conducted in a horizontal position and in a
horizontal direction through a treatment unit, in which the treatment
liquid is directed from above and/or from below on to the circuit board
surfaces. The circuit boards are, in this case, directed past the nozzles
at a small spacing. Within the treatment chamber there are situated the
circuit boards as well as the nozzle openings, preferably within the
treatment solution. In order to move the circuit boards through this
arrangement, transporting devices (rollers or wheels) 14', 14" are
provided, between which the circuit boards 7 are directed (FIG. 8). The
transporting devices extend just like the nozzles, preferably over the
entire width of the circuit boards. Between the transporting devices, the
nozzles 9',9", according to the invention are arranged. The upper
transporting devices 14' are connected with the nozzles 9' in a fixed
unit. While the lower transporting devices 14" and lower nozzles 9" adopt
a secure vertical position, the upper transporting devices and nozzles are
movable in a vertical direction 15, so that differences in thickness in
the circuit boards may be evened out. Since the upper transporting devices
and nozzles are connected with one another, a fixed spacing can be
arranged between the nozzle openings and the circuit board surface.
Instead of circuit boards, other solid bodies or workpieces with fine
openings and recesses can also be treated effectively using the method
according to the invention. For example fine sieves, spinning nozzles or
similar workpieces can be cleaned advantageously.
The following example serves to explain the invention in greater detail.
Blind bores with a diameter of 0.3 mm in circuit board blanks without
copper lamination made from FR4-material(epoxy resin plates strengthened
with glass-fibre mats, FR: flame retardant) and having varying blind bore
depths were to be treated with an aqueous permanganate solution.
The boards contained the holes in individual testing sections with the same
blind bore depths of 0.3 mm, 0.5 mm, 1.0 mm or 2.0 mm within the sections.
The holes were arranged within the 25 mm.times.25 mm testing section
matrix at a spacing of 0.6 mm (mean spacing of the holes) respectively.
The circuit board blanks were conveyed continuously in a horizontal
direction through a treatment unit, in which the boards were aligned in a
horizonal position. The treatment solution was applied from below on to
the circuit board blanks. For this purpose a fine jet-nozzle brush was
used, in the first place, with openings of 0.1 mm diameter and with a 30
mm wide nozzle opening region (entire opening cross-section circa 120
mm.sup.2), said openings being arranged at a distance of 0.5 mm from one
another. Furthermore, there was also in the treatment unit a traditional
splash nozzle stick beneath the plane of movement for the circuit board
blanks, by means of which a strong splash jet of treatment solution was
directed on to the circuit board surface. The spacing of the splash nozzle
from the circuit board surface was 5 mm, the spacing of the fine
jet-nozzle brush from the board 15 mm.
The blanks were moved, in several experiments, through the unit with
feed-in speeds of 0.2 m/min and 0.5 m/min.
In order to evaluate the success of the treatment of the individual holes
in the transparent circuit board material, the wall surface portion within
the holes, which was stained with the permanganate treatment, was assessed
by means of a stereo-microscope in the cross-sectional view of the board.
In the following tables the results of the experiments are reproduced. The
given values represent the portion of the stained surface within the
holes. A smaller portion of stained surface indicates an insufficient
transportation of liquid into the holes.
TABLE 1
(fine jet nozzle)
Passage
Speed Bore Depth Bore Depth Bore Depth
[m/min] 0.3 mm 0.5 mm 1.0 mm
0.2 100% 100% 100%
0.5 100% 100% 100%
TABLE 1
(fine jet nozzle)
Passage
Speed Bore Depth Bore Depth Bore Depth
[m/min] 0.3 mm 0.5 mm 1.0 mm
0.2 100% 100% 100%
0.5 100% 100% 100%
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